Steve, I'm with you on the question of knowing which character is speaking at any given point in a ballad. My experience of singing or listening to repetitious/dialogue ballads is that a good, story-telling singer will automatically point up the speaker with 'said he '/ 'cried she' etc. And I've never heard a duet performance either -- or one that I can remember liking!

And, along with Phil, I'm not enamoured of accompanied versions which create lengthy instrumental interludes for "dramatic tension" -- a good singer has ways of doing that by him/herself. (Although I would trust a few singers to accompany themselves tastefully.)

My own starting point is the unaccompanied ballad, and the amazing performances I've been lucky enough to hear over the years. I've been fortunate enough to hear (in live performance) Jeannie Robertson, Lizzie Higgins, Davie Stewart, Sheila Stewart, and Norman Kennedy: and latterly Gordeanna McCulloch, Heather Heywood, Tom Spiers, Arthur Watson, Adam McNaughtan, Kevin Mitchell et al.
All of these singers are in complete control of the narrative of their ballads and are quite capable of persuading an audience likewise.

End result is that I'm seriously considering working up a presentation of Tam Lin, to appreciate any problems for myself!